Age does matter to some extent. I am 30 years old since January, and a white male. My fiance is 22 and will be 23 very soon, Asian female.
While age has not been a problem for us in our relationship, I do some times worry as a 30 year old white male living in Europe, that is expected to live until the age of 80, what will happen to her, the 22 year old female Asian, who is expected it make it to 90, in the 17 or so years that I will be dead before she dies.
While we are both young, and can have a nice long life together, and it is no time to be talking about death yet. There is a certain responsibility that comes with the age gap and marriage when it comes to these morbid matters.
Age should not really matter as a rule of thumb, it depends on the nature of the relationship. If you are an 18 year old male who wants to meet up with grannies on craigslist for nsa sex, then the 40 year age gap does not matter at all, but if you are both thinking about marriage and a lifetime relationship, or have that as one of your long term relationship goals in life, then once there is say 10 or so years difference, age does come in to play.
As women are generally expected to live longer, if it is an older woman with a younger man, then I would say marriage and a lifetime relationship would get a 15 to 20 year window of difference, as opposed to the 10 year window with an older male and younger female.
If you are just interested in having a bit of fun, experimenting with sex and stuff, and just seeing where it all goes, then I would say that is fine, so long as you don’t lead him on by making him think you too are looking to settle down, there is a chance that is what he is looking for, but even if he is, as a guy he will probably still go along with it for just fun and seeing what it leads to.
All in all, I don’t think there is a problem with 7/8 years or so like in your case.